Re: [Boost-users] PropertyGraphConcept concept checking errors for an example implicit graph

Subject: Re: [Boost-users] PropertyGraphConcept concept checking errors for an example implicit graph
From: W.P. McNeill (billmcn_at_[hidden])
Date: 2010-06-24 21:06:04

How do I "specialize boost::property_map directly"?  This might be the key
to the problem.

My current shot in the dark is to try:

template<>
struct boost::property_map<ImplicitRingGraph, boost::edge_weight_t> {
typedef EdgeWeightMap type;
typedef EdgeWeightMap const_type;
};

which gives me the error

implicit.hpp:116: error: specialization of ‘template<class Graph, class
Property> struct boost::property_map’ in different namespace
/opt/local/include/boost/graph/properties.hpp:244: error:   from definition
of ‘template<class Graph, class Property> struct boost::property_map’

On Thu, Jun 24, 2010 at 5:22 PM, W.P. McNeill <billmcn_at_[hidden]> wrote:

> Thanks for your help.  Getting a little closer.
>
> Once I get the edge properties working I'll look at traversal concepts
> other than AdjacencyGraphs.  So far this has been the easy part for me.
>
> I have been looking at the grid graph, but I couldn't figure out how to add
> weights to the edges of a grid graph.  I can't find a simple example of an
> implicit graph with properties.  (Which is why I'm trying to write one now.)
>
> What do you mean by "Write an empty struct that inherits from all of the
> ones that you are going to model"?  I didn't think there were concept base
> classes to inherit from.
>
> Changing the property typedef in the implicit graph struct to
>
>     typedef boost::property<boost::edge_weight_t, float>
> edge_property_type;
>
> making the get() functions take constant graph object references, and
> checking against the ReadablePropertyGraphConcept improves the compilation.
>  I now no longer have pages of errors, which makes me think I'm on the right
> track.
>
> I still have two errors, both of which I'm confused about.
>
> 1. graph_concepts.hpp:390: error: conversion from ‘EdgeWeightMap’ to
> non-scalar type ‘boost::typed_identity_property_map<size_t>’ requested
>
> This is the same as before.  This error makes me feel like I've got the
> wrong return value for one of my get() functions, but after double-checking
> they look right.
>
>
> 2. property_map.hpp:318: error: no match for ‘operator[]’ in ‘(const
> boost::typed_identity_property_map<size_t>&)((const
> boost::typed_identity_property_map<size_t>*)(& pa))[k]’
>
> I didn't think any concept required operator[], so I'm not sure why this is
> happening.  Line 318 is inside the inline get() function of
> the put_get_helper(), but I'm not using put_get_helper() in my code.
>
>
> On Thu, Jun 24, 2010 at 1:25 PM, W.P. McNeill <billmcn_at_[hidden]> wrote:
>
>> I am writing a stripped-down implicit graph that I hope can be a useful
>> template for others working with the Boost Graph library.  The project is
>> hosted at github.  Excerpts from the source are in this email, and the full
>> source is viewable online at
>> http://github.com/wpm/Boost-Implicit-Graph-Example.
>>
>> I am currently getting errors from the concept checking code which I don't
>> understand and am looking for suggestions as to what I am doing wrong.
>>
>> This is graph class.
>>
>> struct ImplicitRingGraph {
>> ImplicitRingGraph(size_t n):n(n) {};
>>
>> // Graph concept
>>  typedef size_t vertex_descriptor;
>> typedef boost::undirected_tag directed_category;
>>  typedef boost::disallow_parallel_edge_tag edge_parallel_category;
>> typedef boost::adjacency_graph_tag traversal_category;
>>
>> // AdjacencyGraph concept
>> typedef RingAdjacencyIterator adjacency_iterator;
>>
>> // PropertyGraph concept
>> typedef boost::edge_weight_t edge_property_type;
>>
>> // Additional types required by the concept-checking code.
>> typedef std::pair<vertex_descriptor, vertex_descriptor> edge_descriptor;
>>  typedef size_t vertices_size_type;
>> typedef size_t edges_size_type;
>> typedef size_t degree_size_type;
>>  typedef void out_edge_iterator;
>> typedef void in_edge_iterator;
>>  typedef void vertex_iterator;
>> typedef void edge_iterator;
>>
>> // The number of vertices in the graph.
>>  size_t n;
>> };
>> typedef boost::graph_traits<ImplicitRingGraph>::edge_descriptor Edge;
>>
>>
>> I want the edges to have weights, so it models the PropertyGraph concept.
>>  The following functions implement the valid expressions.
>>
>>
>> EdgeWeightMap get(boost::edge_weight_t, ImplicitRingGraph& g) {
>>  return EdgeWeightMap();
>> }
>>
>>
>> EdgeWeight get(boost::edge_weight_t tag, ImplicitRingGraph& g, Edge e) {
>>  return get(tag, g)[e];
>> }
>>
>>
>> (Definitions of Edge, EdgeWeight, and EdgeWeightMap are visible online.  I
>> also define an adjacency iterator that is not shown here.)
>>
>> I can write code that reads an edge weight.
>>
>> ImplicitRingGraph g(5);
>>  EdgeWeightMap m = get(boost::edge_weight, g);
>> boost::graph_traits<ImplicitRingGraph>::edge_descriptor e(0, 1);
>>  EdgeWeight w = get(boost::edge_weight, g, e);
>>
>> However I get errors when I try to use the concept checking code.
>>
>>  function_requires<
>> PropertyGraphConcept<ImplicitRingGraph,
>>  Edge,
>>  edge_weight_t>
>> >();
>>
>>
>> The full error printout is huge, but there appear to be three relevant
>> problems.
>>
>> 1. graph_concepts.hpp:406: error: conversion from ‘EdgeWeightMap’ to
>> non-scalar type ‘boost::typed_identity_property_map<size_t>’ requested
>>
>> The line in graph_concepts.hpp is
>>
>>         Map pmap = get(Property(), g);
>>
>> inside the concept check for PropertyGraph.  It looks to me like I have a
>> function to handle this.  I don't understand
>> where boost::typed_identity_property_map<size_t> is coming from.
>>
>>
>> 2. graph_concepts.hpp:408: error: no matching function for call to
>> ‘put(boost::edge_weight_t, ImplicitRingGraph&, Edge&, size_t&)’
>>
>> I didn't write any put() functions so I understand why I'm getting this.
>>  However, I would like the edge weights to be readable but not writeable
>> (myEdgeWeightMap models a ReadablePropertyMap), and I can't figure out how
>> to specify the read-only property in the graph defintion.
>>
>>
>> 3. graph_concepts.hpp:390: error: no matching function for call to
>> ‘get(boost::edge_weight_t, const ImplicitRingGraph&)’
>> graph_concepts.hpp:391: error: no matching function for call to
>> ‘get(boost::edge_weight_t, const ImplicitRingGraph&, Edge&)’
>>
>> Should I create functions identical to what  I've already written, except
>> with constant modifiers in front of the graph type?  That feels like
>> redundant source.
>>
>>
>>  Thanks for any help you can give.  Hopefully, a completed version of this
>> example would be a useful resource for other BGL developers.
>>
>
>